Production of hydrocarbon fuels



Patented May 22, 1945 UNITED STATES 1 PATENT orrics.

PRODUCTION OF HYDROCABBON FUELS William E. Bradley, Los Angeles, Calif., assignor to Union Oil Company of California, L08 Angcles, Calif., a corporation of California No Drawing. Application March 19, mo,

, Serial No. szasos Claims. (oi. zoo-sass) .This' invention relates to a process for manufacturing hydrocarbon motor fuel and more -speciflcally pertains to the production of hydrocarbon fuels of an isoparaillnic character particularly suitable for use in automobile and aviation engines. The present specification is a continuation in part of my co-pendlng application Serial No. 202,723 filed April 18, 1938.

It is the main object'of this invention to provide a simple method for producing, by physical treatment of raw materials and subsequent controlled chemical reactions thereof, a gasoline of improved volatility characteristics and antiknock rating.

Owing to the adoption of high compression ratios in automobile and aviation gasoline engines. an insistent demand has been made upon petroleum refiners and similar industries .to furnish motor fuels which have high anti-knock values. Thus, in the aviation industry many specifications require a gasoline having an anti-knock rating of about 100 iso-octane (as-determined by the A. S. T. M. method) and containing not more than 3 milliliters of tetraethyl lead per gallon of such gasoline. This demand for fuels of unparailinic hydrocarbons, the normal or straight chain hydrocarbons boiling above normal pentane' being of comparatively low anti-knock value.

Automobile and aviation fuels, particularly the latter, are comprised to a large extent of hydrocarbons having 7, B and 9 carbon atoms, and may contain also hydrocarbons having as high as 12 carbon atoms. A minor proportion of, the gaso-.

line is comprised of hy'drocarbonshaving 5 and 6 carbon atoms, but this portion is essential and its properties are of importance because of their direct influence on the starting characteristics of the gasoline.

Previously, as disclosed in my co-pending application, I have discovered that branched-chain hydrocarbons containing '7, 8 and 9 carbon atoms can be readily formed by an alkylation process comprising reacting propylene, butylenes and pentenes with iso-butane in the presence of concentrated sulfuric acid. Due to side reactions.

some branched-chain hydrocarbons containing 6 and 10 or more carbon atoms are also formed but the product, although of especially high antiknock rating dos not possess the proper volatility characteristics, as indicated by the En ler disusually high anti-knock quality is due primarily to the high payload efficiency which may be realized in commercial aviation and to certain definite-tactical advantages to be gained in military aviation when motor fuels of this type are employed.

The use of knock inhibitors, for example, tetraethyl lead, aniline, iron carbonyl, nickel carbonyl. etc., are effective in various degrees in increasing the anti-knock rating of gasolines but the use.

of these compounds is limited due to certain inherent disadvantages, such as toxic effects and tendencies to crystallize out at lowtemperatures.

- to form sludge, to corrode engine parts, etc. Olefin and aromatic hydrocarbons are known to possess high anti-knock values but it has been considered advisable to limit the percentages of such compounds which maybe present in gaso-' lines, at least in the case of aviation fuels, to negligible amounts;

The foregoing limitations therefore make it es-, sential to produce fuels consisting primarily of stable hydrocarbons of inherently high anti-.

knock value. It is now well recognized that such hydrocarbons comprise the" branched-chain tillation, to make it a desirable fuel for present type internal combustion engines. In preparing an acceptable gasoline from such an alkylation tillation characteristics but lowered anti-knockrating and requiring the addition of a knock inhibitor, such as tetraethyl lead, in order to give a material having the same anti-knock rating as the original alkylation product.

Further, in my co-pending application mentionedjhereinabove, it is noted that isopentane likewise will react with olefin: to produce higherboiling branched-chain fparaflin hydrocarbons as the catalyst.

I have now discovered that in producing a gasoline by,the alkylation process, a material of the desired volatility can be directly prepared, withoutthe necessity for extraequipment, by employing olefin and isoparamn fractions that contain a quantity of relatively unreactive hydrocarbons having and 6 and under some circumstances possibly more carbon atoms. I. have further discovered that by reacting a-mixture of isopentane and isobutane witholefins, particu-- larly the normally gaseous olefins, and subsequent fractionation, I can take-advantage of their above noted difference in reaction rates and roduce in a single operation a gasoline of improved distillation and volatility characteristics and comprised substantially of all branched-chain paraflinic hydrocarbons, said gasoline having an anti-knock rating equivalent to that of the usual alkvlation gasoline produced by reacting the same olefins with isobutane alone, Furthermore, by regulating the proportions of isobutane, isopentane and olefins, I can obtain additional control of the character of the alkylation product; in general, by maintaining a high molal ratio of isobutane to isopentane and a high molal ratio oi isobutane plus isopentane to olefin in the reaction mixture, the reacting olefins will combine primarily with isobutane and only to a minor extent with isopentane, with the result that the product obtained after stabilization to removematerials boiling below isopentane will contain ventionto produce a gasoline comprised essentially of branched-chain-hydrocarbons and requiring the addition of no, or only a minimum of, straight-run gasoline in order to yield a. product of desired volatility and Engler distillation characteristics. It is another object to produce a taining fraction suitable for the purposes of the of 10 to 1 or it may even be as high as 95-100 to l. Forexample, suppose 95 mols of isobutane and 5 mols of isopentane were reacted with 10 mols of isobutylene. After stabilization to remove materials boiling below isopentane, the m sultant product would contain 10 mols of higher boiling branched-chain hydrocarbons and approximately 5 mols of isopentane. Actually the amount of isopentane present would be slightly less due to reaction-of a small proportion of the isopentane with isobutylene. It can be seen that by decreasing the molal ratio of isobutane plus isopentane to isobutylene or decreasing the ratio of isobutane to isopentane, maintaining the molal ratio of isobutane plus isopentane to olefin constani, the proportion of isopentane in the stabilized product can be readily decreased ,to any desired extent.

The olefin-containing fraction to be reacted with the isoparaflin fraction may be comprised of various olefins as indicated in my previous application but for the purpose of the present example this fraction must contain substantially no cyclic or straight-chain parafiin hydrocarbons boiling above isopentane. A typical olefin-conpresent invention would be the gases derived from the stabilization of pressure distillate. Such a material is normally comprised of hydrocarbons boiling below isopentane and may contain as much as 50% of propylenes and butylenes. If it is desired, however, the olefin fraction may contain I pentenes and isopentane-but fractionation must gasoline comprised substantially of branchedchain hydrocarbons and having a relatively high vapor pressure; said gasoline being formed by reacting a mixture of isobutane and isopentane with olefins under'such conditions that only a part of the isopentane is alkylated and subsequently fractionated to remove hydrocarbons boiling below isopentane.

Briefly, where'it is desired to produce directly .a gasoline of improved volatility and comprised essentially of only branched-chain hydrocarbons, my preferred process may be described as follows:

An isoparaflln fraction comprised of isobutane and isopentane is obtained by distillation or other.

means'from a suitable stock, such as, for example c natural gasoline. This fraction will usually cone tain normal butane also and possibly propane but must be sufllciently closely fractionated so as not to contain any appreciable percentage of normal pentane for reasons which will be apparent hereinafter. The molal ratio" of isobutane to isopentane may vary over aconsiderable range, "depending upon the percentage of isopentane desired in the final product and'the molal ratio, of

' isobutane plus isopentane to reacting olefins, but the ratio should be preferably not less than 1 to 1 be sufliciently good so that the material contains little or no normal pentane or higher boiling paraflinic and cyclic hydrocarbons. If there is an appreciable proportion of isopentane present in the olefin-containing fraction then the isobutaneisopentane mixture with which it is to be reacted may contain a correspondingly smaller proportion of isopentane and may even contain no isopentane, it only being necessary that the mixture of olefin and isoparaflin fractions coming into con- V tact with the catalyst in the reaction zone contain isobutane, isopentane and olefins in the desired. proportions. 0

Normally, in order to prevent polymerization 1 invention the number of mols of isobutane plus the number of mols of isopentane should be at least threeto five times as great as the number of mols of olefins present in the reaction zone and preferably even higher. In conducting the alkylation reaction the olefin-containing fraction and the isobutane-isopentane fraction are brought to-' gether in the presence of an alkylation catalyst for the reactionto complete itself, the catalyst is separated from the hydrocarbon product and the latter fractionated to remove materials boiling below isopentane. The residual material may be 1 further fractionated, ifdesired, in order to remove a high boiling alkylation products. For example,

' and it is desirable that-it should be of the order in producing gasoline for use 'in aviation engines.

those hydrocarbons boiling above about 320 F, areusuallyremoved by distillation. 'The resultant aviation gasoline will be comprised wholly of.

branched-chain parafiinic hydrocarbons and will contain a substantial portion of isopentane.

' It is immediately evident from a consideration of the above description of my preferred process and the boiling points of isopentane and normal pentane that if any apreciable proportion of the latter, or other higher boiling hydrocarbons of low anti-knock rating, was present in the stocks introduced into the reaction zone, it would be present in the finished gasoline and as a consequence would-lower the anti-knock rating of the product. y

In the foregoing discussion concentrated sulfuric acid has been used as illustrative of an alwlation catalyst, but for the purposes of the present invention, it is evident that any other type of alkylation catalyst, such as for example, aluminum chloride, boron trifiuoride, etc., could likewise be used with equal facility without altering the scope of the invention. Auminum chloride will catalyze the addition of oleiins to normal paramns and naphthenes but as the reaction with isobutane is more rapid, 'by maintaining an excess of the latter, the character of the product can be readily controlled by the processes described hereinabove.

Further, it can be seen from the foregoing description that where it is desired to obtain a maximum degree of control on the character of the more volatile fractions in the finished alkylation product, unreactive hydrocarbons containing 5, 6 and even 7 carbon atoms can be included in either the reacting olefin or isoparaflln fraction or both.

Other features, advantages and objects of the present invention will become apparent to those skilled in the art from the following specific examples:

Example 1 By the stabilization of natural gasoline and pressure distillate, respectively, isobutane and oleiln containing fractions of the following compositions were prepared:

Isobutane Olefin fracggf g tion, per cent y W] by vol.

Approximately 5.11 gallons per hour of the isobutane fraction and 1.25 gallons per hour of the olefin fraction were mixed with a recycled hydrocarbon stream, as indicated below, and subsequently intimately contacted with sulphuric acid or approximately 98% H2804 content. The reaction mixture was passed into a settling chamber and allowed to separate into two phases, an

suiiicient pressure, approximately 90 poundsper' square inch, to maintain the reactants in a liquid state. An amount of reaction product equivalent to the amount of olefin and isoparaflin fractions introduced into the system was continuously withdrawn and stabilized to remove materials boiling below isopentane.

The composition of the stabilized reaction product was as follows:

The stabilized material contained substantially no olefinic or aromatic hydrocarbons and had a knock-rating (as determined by the A. S. T. M. method) of 90.

Example 2 The procedure described in Example 1 was repeated using stocks which contained substantially no hydrocarbons boiling above normal butane. The resultant stabilized reaction product had the following composition:

The stabilized product contained substantially no olefinic or aromatic hydrocarbons and had a knock-rating of 89.

A comparison of the results of the two above described experiments discloses a considerably higher volatility for the product prepared from the fractions containing a mixture of both isobutane and isopentane and it will be noted that such increase in volatility was obtained without any loss in knock-rating.

The foregoing description of my invention is not to be construed as limiting but only as illustrative of the invention as many variations may be made within the scope of the following claims.

I claim:

1. A process for the production of isoparafflnic motor fuels of improved volatility and antidetona'tion characteristics which comprises subjecting a hydrocarbon feed stock boiling completely below the boilingpoint of normal pentane and containing olefins, isobutane, and isopentane, to alkylation in the presence of an' alkylation catalyst, and separating directly from the reaction product by distillation a fraction consisting of unreacted isopentane and products of the alkylation reaction boiling above normal butane and substantially free of normal pentane; the molal proportions of olefins, isobutane and isopentane in said hydrocarbon feed stock being such that the ratio of isobutane to isopentane is at least 1 to l; and the ratio of isobutane plus isopentane to olefin is at least 3 to 1.

2. A process according to claim 1 in which the olefins consist of butenes.

3. A process according to claim 1 in which the alkylation catalyst is concentrated sulfuric acid. v

4. A method of producingmotor :fuel which comprises reacting an isoparaiunic feed alkylation catalyst, and separating directly from' the resulting mixture by distillation a fraction acre-s72 bon'mixture containing said amyleneisopentanq normal p'entane and. another amylene higher boiling than normal pentane is used as the source T of the said iower boiling amylene, the method oi comprising allwlated hydrocarbons substantially tree of normal pentane and containing a sub stantial proportion of nnreacted isopentane; the

molal proportions of isobutane, isopentane and butylenes in the reaction mixture/being such that the ratio of isobutane to isope'ntane is at least 1 to l, and the-ratio of isobutane plus isopentens to butylene is at least 3 to 1.

5. In a processor producing a motor fuel by alkylating 'isobutane with-an amylene lower boiling than .normal pentane, wherein a hydrocarbutane in the presence-of an alkylation cata .lyst under alkylating conditions and recover-1 isobutane.

' increasing the yield .of desirable isobutane alkylv I ation products and the quality of the hydrocarbon components of the reaction mixture boiling in the gasoline range which comprises distilling said hydrocarbon mixture to'separate an-isopentane-amylene traction substantiallyfree from said normalpentane and higher boiling amylene, reacting the separated fraction .with isoing a. substantially isoparaflinic-mixture containing iso-pentane and alkylationfproducts of E. BRAD: LEY' 

